Transcript A Hitch-Hiker*s Guide to the LEP3 RF System

RF system for LEP3 and TLEP
Andy Butterworth (CERN BE/RF)
Thanks to E. Ciapala, R. Calaga, E. Montesinos, O.
Brunner, P. Baudrenghien, S. Claudet
Overview
• Introduction and general considerations
– A bit of history: the LEP2 RF system
– Cryogenic cooling capacity
• Technology choices: which is the best fit for a 120
GeV e+e- storage ring?
–
–
–
–
Producing the voltage
Handling the RF power
Damping higher order modes
Controlling the impedance: Low Level RF
• Tentative conclusions
LEP2 SC RF system
RF frequency
352 MHz
Number of cavities *
288
Total accelerating voltage *
3500 MV
Number of klystrons *
36
Total cryomodule length
812 m
Cavities per klystron
8
Average (nom.) power per klystron
0.6 (1.3) MW
Average power per cavity
90 kW
* Plus 56 copper cavities (130 MV) driven by 8 klystrons
Circumference
26.7 km
Beam energy
104.5 GeV
Energy loss per turn
3.4 GeV
Beam current
5 mA
Synchrotron radiation power
17 MW
Available cooling power
53 kW @ 4.5K
LEP2 SC RF system
Circumference
26.7 km
Beam energy
104.5 GeV
Energy loss per turn
3.4 GeV
Beam current
5 mA
Synchrotron radiation power
17 MW
Available cooling power
53 kW @ 4.5K
Design gradient 6 MV/m
RF frequency
352 MHz
Number of cavities *
288
Total accelerating voltage *
3500 MV
Number of klystrons *
36
Total cryomodule length
812 m
Cavities per klystron
8
Average (nom.) power per klystron
0.6 (1.3) MW
Average power per cavity
90 kW
* Plus 56 copper cavities (130 MV) driven by 8 klystrons
1999
2000
1998
Introduction
The RF system of an e+e- collider has to:
• replace the energy lost U0 at each turn by synchrotron
radiation
– total power needed by the beam = U0 x Ibeam
~
• maintain longitudinal focusing with sufficient momentum
acceptance ||max,RF to keep a good beam lifetime, given
– the equilibrium energy spread due to quantum
excitation/radiation damping (quantum lifetime)
– the energy spread (tail) due to beamstrahlung
RF voltage
– 4% for LEP3
– 3% for TLEP-H
100
LEP3:
U0 = 7.0 GeV
p = 8.1 x 10-5
E0 = 120 GeV
Jz = 1.5
80
q hours
• Quantum lifetime is a very steep
function of VRF
• RF voltage is defined by the
momentum acceptance needed to
cope with beamstrahlung
60
40
fRF = 352 MHz
fRF = 704 MHz
fRF = 1300 MHz
20
0
7.0 10 9
LEP3
VRF [GV]
for
τq = 100h
VRF [GV]
for
δmax,RF = 4%
8
352
7.4
8.8
6
704
7.7
10.0
1300
8.1
11.7
10 9
9.0
10 9
1.0
10 10
1.1
10 10
1.2
10 10
10 10
1.1
10 10
1.2
10 10
VRF V
RF
frequency
[MHz]
max,RF
Machine
8.0
fRF = 352 MHz
fRF = 704 MHz
fRF = 1300 MHz
4
2
δmax,RF ~ fRF-1/2 for a
given RF voltage
0
7.0
10 9
8.0
10 9
9.0
10 9
1.0
VRF V
Parameters: LEP3 (27 km ring) and
TLEP (80 km ring)
beam energy Eb [GeV]
circumference [km]
beam current [mA]
#bunches/beam
#e−/beam [1012]
bending radius [km]
partition number Jε
momentum comp. αc [10−5]
SR power/beam [MW]
ΔESRloss/turn [GeV]
VRF,tot [GV]
δmax,RF [%]
fs [kHz]
Eacc [MV/m]
eff. RF length [m]
fRF [MHz]
δSRrms [%]
σSRz,rms [cm]
LEP2
104.5
26.7
4
4
2.3
3.1
1.1
18.5
11
3.41
3.64
0.77
1.6
7.5
485
352
0.22
1.61
LEP3
120
26.7
7.2
4
4
2.6
1.5
8.1
50
6.99
12
4.2
3.91
20
600
1300
0.23
0.23
TLEP-Z
45.5
80
1180
2625
2000
9
1
9
50
0.04
2
4
1.29
20
100
700
0.06
0.19
TLEP-H
120
80
24.3
80
40.5
9
1
1
50
2.1
6
9.4
0.44
20
300
700
0.15
0.17
TLEP-t
175
80
5.4
12
9
9
1
1
50
9.3
12
4.9
0.43
20
600
700
0.22
0.25
RF: General considerations for LEP3 and
TLEP-H
LEP3
TLEP-H
Top-up injector rings
RF voltage
12 GV (δmax,RF = 4.2%)
needed for beamstrahlung
6 GV (δmax,RF = 5.7%)
needed for beamstrahlung
LEP3:
9 GV
TLEP-H: 2.5 GV
for quantum lifetime
Gradient
High ( ≥ 20 MV/m?)
Overall length of the RF
sections, available space in
the LHC tunnel.
Moderate, as the space
constraints are less
important, required RF
voltage is lower.
High, to keep the RF
sections short (cost, space).
Tradeoff with cryogenic
power.
Defined by beam power
considerations.
Cryogenic power less critical
(low duty cycle)
High power throughput per
cavity to supply the
required 100 MW of SR
power.
The same 100 MW total
power throughput.
Maximum power rating of
the input couplers dictates
the number of cavities and
gradient.
SR power low (kW per
cavity) due to low beam
currents.
RF power
Power dominated by
acceleration during energy
ramp.
General considerations (2)
• RF frequency:
– higher is better, for short bunch length (hourglass effect)
• Higher order mode power:
– cavity loss factors, bunch length, bunch charge, beam current
– power limits of HOM damping
– bunch break-up from transverse modes
• RF power sources:
– klystrons, IOTs, solid state amplifiers?
– available power, efficiency, cost
• Feedbacks and Low-Level RF:
– beamloading (especially if no top-off injection)
– longitudinal impedance control (coupled bunch modes)
LHC cryogenic plant capacity
• For LEP3 it would be very advantageous if the cryogenic power required
for the RF could be supplied by the existing LHC cryogenics plants
Installed refrigeration capacity in the LHC sectors
Temperature
level
•
•
•
High-load Low-load
sector
sector
(1-2, 4-5,
(2-3, 3-4,
5-6, 8-1)
6-7, 7-8)
33000
31000
50-75 K
[W]
4.6-20 K
[W]
7700
7600
4.5 K
[W]
300
150
1.9 K LHe
[W]
2400
2100
4 K VLP
[W]
430
380
20-280 K
[g.s-1]
41
27
LHC cold compressors (125 g/s@15mbar=1.8K) have similar dimensions as the CEBAF ones
(250g/s@30mbar=2.0K)
However, piping, motors and so on would not be compatible with a factor 2 in capacity.
A more detailed study would be necessary to evaluate the performance we could have if
some parts would be changed (motors, bearings, valves,...)
Total wall-plug power for LHC
cryogenics = 40 MW
Temperature: Why 2K not 4.5?
RF surface resistance Rsurf = Rres + RBCS
BCS surface
resistance
Residual resistance
(impurities, trapped flux,
etc.)
Increases with
frequency
Increases with
temperature
Gradient and dynamic heat load
Shorter RF sections 
Q-slope
Lower Q0, higher
dissipation 
margin for
microphonics
etc.
Power dissipation =
Q0 depends on losses
in cavity walls
R/Q depends only on
cavity geometry
LEP3/TLEP RF: Potential options
ILC collaboration
1300 MHz 9-cell cavity
ESS, eRHIC, SPL
SPL type cryomodule
704 MHz 5-cell cavity
Option 1: 1.3 GHz TESLA/ILC
• ILC cavity performance requirements:
Gradient
Q0
Vertical test (bare cavity)
35 MV/m
> 0.8 x 1010
Mounted in cryomodule
31.5 MV/m
> 1.0 x 1010
Test results for eight
1.3 GHz 9-cell TESLA
cavities achieving the
ILC specification
(DESY)
(mounted)
BCP + EP
Option 1: 1.3 GHz TESLA/ILC
• Promise of even higher cavity performance in future
– ongoing R&D in new techniques
– e.g. large grain and single crystal niobium cavities
Large-grain 9-cell cavities at DESY
Single-crystal 9-cell cavities at DESY
D. Reschke et al. SRF2011
A Brinkman et al. SRF07
Option 1: 1.3 GHz (LEP3)
LEP3
1300 MHz
9-cell
Collider Accel.
ring
ring
Gradient [MV/m]
20
25
Active length [m]
1.038
1.038
Voltage/cavity [MV]
20.76
25.95
Number of cavities
579
463
Total cryomodule length [m]
927
737
1036
1036
1.5
1.3
Heat load per cavity [W]
27.7
50.0
Total heat load [kW]
16.1
23.2
Heat load per sector [kW]
2.0
2.9
Accel. ring @ 10% DF [kW]
0.15
0.22
R/Q [linac ohms]
Q0 [1010]
RF power per cavity [kW]
Matched Qext
173
216
2.4E+06
3.0E+06
VRF [GV]
12
9
PSR [MW]
100
1
cf. LEP2: 812 m
cf. LHC cryoplant capacity @ 1.9K
of 2.4 or 2.1 kW per sector
Input power couplers which
can handle these CW power
levels?
1.3 GHz power couplers
• TTF-III couplers tested
to 5 kW in CW
– 8kW with improved
cooling (BESSY)
• Some higher power
adaptations for ERL
injectors
– e.g. Cornell 60 kW CW
2 couplers per 2-cell cavity in ERL injector cryomodule
Gradient: 5-15MV/m
Beam current: 100 mA
V. Vescherevitch, ERL’09
Developing a power coupler for 1.3 GHz high gradient and
200 kW CW looks challenging…
Option 2: 704 MHz eRHIC/SPL
• BNL 5-cell 704 MHz test cavity
(A. Burill, AP Note 376, 2010)
SPL/ESS design value
2.0 x 1010 @ 20MV/m
BCP only
•
•
First cavities, lots of room for
improvement
Measurement after only BCP
surface treatment (no EP cf. TESLA
cavities)
•
JLab 748 MHz Cavity Test for highcurrent cryomodule
BCP only
Option 2: 704 MHz (LEP3)
LEP3
704 MHz
5-cell
Gradient [MV/m]
20
Active length [m]
1.06
Voltage/cavity [MV]
21.2
Number of cavities
567
Total cryomodule length [m]
902
R/Q [linac ohms]
506
Q0 [1010]
2.0
Heat load per cavity [W]
44.4
Total heat load [kW]
25.2
Heat load per sector [kW]
3.1
Accel. ring @ 10% DF [kW]
0.24
RF power per cavity [kW]
176
Matched Qext
5.0E+06
Collider Accel.
ring
ring
VRF [GV]
12
9
PSR [MW]
100
1
cf. LEP2: 812 m
higher heat load despite higher Q0
because of lower R/Q
cf. LHC cryoplant capacity @ 1.9K
of 2.4 or 2.1 kW per sector
Input power couplers at 704
MHz for these power levels?
704 MHz power couplers
• CEA Saclay HIPPI water cooled
coupler (SPL/ESS)
– tested up to 1.2 MW 10% duty
cycle in travelling wave, and 1 MW
in standing wave
• CERN SPL air-cooled single
window coupler
– 2 designs currently under test:
cylindrical and planar disk windows
– design goal: 1 MW 10% duty cycle
for SPL
– cylindrical window design uses LHC
coupler ceramic window with
tapered outer conductor
– LHC windows are routinely tested
to > 500 kW CW
Cylindrical
ceramic window
Coaxial disk
ceramic window
E. Montesinos
704 MHz power couplers
Latest R&D results
High average power air cooled couplers (CERN BE-RF-PM)
• Cylindrical window :
▫ TW : 1000 kW 2 ms 20 Hz
▫ SW : 550 kW 500 us 8 Hz
• Coaxial disk window :
▫ TW : 1000 kW 2 ms 20 Hz
▫ SW : 1000 kW 1.5 ms 20 Hz
40 kW average power
40 kW average power
Limited by arcing on air side of
window
Limited by losses in uncoated
outer double walled tube
 Improvements in window air
flow and screen at braze
 Improvements in coating
TLEP-H
TLEP-H
1300 MHz
9-cell
704 MHz
5-cell
Gradient [MV/m]
20
25
20
Active length [m]
1.038
1.038
1.06
Voltage/cavity [MV]
20.76
25.95
21.2
Number of cavities
290
232
284
Total cryomodule length [m]
470
368
457
1036
1036
506
1.5
1.3
2.0
27.7
50.0
44.4
8.0
11.6
12.6
Heat load per sector [kW]
1.01
1.45
1.58
Accel. ring @ 10% DF [kW]
0.04
0.06
0.07
RF power per cavity [kW]
344.8
431.0
352.1
1.2E+06
1.5E+06
2.5E+06
R/Q [linac ohms]
Q0 [1010]
Heat load per cavity [W]
Total heat load [kW]
Matched Qext
Collider Accel.
ring
ring
VRF [GV]
6
2.5
PSR [MW]
100
1
cf. LEP2: 812 m
• Limited by power per
cavity
• Install twice the # cavities
with half the gradient?
Very high power levels!
(2 x LEP3)
Parameters: LEP3 (27 km ring) and
TLEP (80 km ring)
beam energy Eb [GeV]
circumference [km]
beam current [mA]
#bunches/beam
#e−/beam [1012]
bending radius [km]
partition number Jε
momentum comp. αc [10−5]
SR power/beam [MW]
ΔESRloss/turn [GeV]
VRF,tot [GV]
δmax,RF [%]
fs [kHz]
Eacc [MV/m]
eff. RF length [m]
fRF [MHz]
δSRrms [%]
σSRz,rms [cm]
LEP2
104.5
26.7
4
4
2.3
3.1
1.1
18.5
11
3.41
3.64
0.77
1.6
7.5
485
352
0.22
1.61
LEP3
120
26.7
7.2
4
4
2.6
1.5
8.1
50
6.99
12
4.2
3.91
20
600
1300
0.23
0.23
TLEP-Z
45.5
80
1180
2625
2000
9
1
9
50
0.04
2
4
1.29
20
100
700
0.06
0.19
TLEP-H
120
80
24.3
80
40.5
9
1
1
50
2.1
6
9.4
0.44
20
300
700
0.15
0.17
TLEP-t
175
80
5.4
12
9
9
1
1
50
9.3
12
4.9
0.43
20
600
700
0.22
0.25
Top-up injector rings
• SR power very small
– (beam current ~ 1% of collider ring)
• Average cryogenic heat load very small
– (duty cycle < 10%)
• Power is dominated by ramp acceleration:
– for a 1.6 second ramp length:
LEP3
TLEP-H
TLEP-t
Beam current [mA]
0.14
0.48
0.054
Energy swing [GeV]
100
100
155
Max. SR power/cavity [kW]
6.2
8.5
6.2
Acceleration power [kW]
32
100
18
Max. power per cavity [kW]
38
109
24
Well within our 200 kW budget
Higher order mode power
R. Calaga
Cavity loss factors
Average PHOM = k||.Qbunch.Ibeam
k|| = 8.19 V/pC
LEP3
k|| = 2.64 V/pC
TLEP-H
Beam current [mA]
14.4
24.3
Bunch charge [nC]
160
41
HOM power (704
MHz cavities) [kW]
6.1
10.4
HOM power (1.3
GHz cavities) [kW]
18.8
32.3
• HOM powers in the kW range to remove from the cavity at 2K
HOM power “league table”
Project
Average
Beam HOM
current power per
[mA] cavity [W]
CEBAF 12GeV
Project X
XFEL
SPL
APS SPX
BERLinPro
KEK-CERL
Cornell ERL
eRHIC
KEKB
LEP3 704 MHz
TLEP-H 704 MHz
LEP3 1.3 GHz
TLEP-H 1.3 GHz
After M. Liepe, SRF2011
0.10
1
5
40
100
100
100
100
0.05
0.06
1
22
2,000
150
185
200
300
1,400
7,500
15,000
14
49
14
49
6,100
10,400
18,800
32,100
KEKB SC cavity HOM dampers
• 509 MHz single cell cavity
• Iris diameter 220 mm
• Ferrite HOM absorbers on both
sides (outside cryostat)
• HOM power: 16 kW/cavity
Y. Morita et al., IPAC10, Kyoto
HOM power “league table”
Project
Average
Beam HOM
current power per
[mA] cavity [W]
CEBAF 12GeV
Project X
XFEL
SPL
APS SPX
BERLinPro
KEK-CERL
Cornell ERL
eRHIC
KEKB
LEP3 704 MHz
TLEP-H 704 MHz
LEP3 1.3 GHz
TLEP-H 1.3 GHz
After M. Liepe, SRF2011
0.10
1
5
40
100
100
100
100
0.05
0.06
1
22
2,000
150
185
200
300
1,400
7,500
15,000
14
49
14
49
6,100
10,400
18,800
32,100
eRHIC /SPL/ESS
704 MHz cavities
5-cell SRF cavity with strong
HOM damping for eRHIC at BNL
HOM high-pass filter
HOM ports
F = 703.5MHz
HOM couplers: 6 of antenna-type
Fundamental supression: two-stage high-pass filters
Eacc = 20 MV/m
Design HOM power: 7.5 kW
FPC port
 BNL3 cavity optimized for high-current applications such as eRHIC and SPL.
 Three antenna-type HOM couplers attached to large diameter beam pipes at each end of the cavity
provide strong damping
 A two-stage high-pass filter rejects fundamental frequency, allows propagation of HOMs toward an RF
load.
M. Tigner, G. Hoffstaetter, SRF2011, W. Xu et al, SRF2011
HOM power “league table”
Project
Average
Beam HOM
current power per
[mA] cavity [W]
CEBAF 12GeV
Project X
XFEL
SPL
APS SPX
BERLinPro
KEK-CERL
Cornell ERL
eRHIC
KEKB
LEP3 704 MHz
TLEP-H 704 MHz
LEP3 1.3 GHz
TLEP-H 1.3 GHz
After M. Liepe, SRF2011
0.10
1
5
40
100
100
100
100
0.05
0.06
1
22
2,000
150
185
200
300
1,400
7,500
15,000
14
49
14
49
6,100
10,400
18,800
32,100
due to higher beam
intensity.
 needs study
RF power sources
• “Super-power”
klystrons at 700
MHz
• Multiple cavities
per klystron as in
LEP2
• Could perhaps use
IOTs (inductive
output tubes) or
solid state
amplifiers for the
injector ring (lower
power required)
Type
Output
Frequency
Power
(MHz)
(kW)
VKP-7952B 704
1000
Efficiency
(%)
65
Type
Output
Frequency
Power
(MHz)
(kW)
Efficiency
(%)
E3732
508.6
1200
63
E37701*
1071.8
1200
63
Type
Output
Frequency
Power
(MHz)
(kW)
Efficiency
(%)
TH2178
508.6
62
1200
LLRF: instabilities and feedbacks
• LEP2:
– slow scalar sum feedback acting on the
klystron modulation anode, with the
klystrons operated at saturation for
maximum efficiency
• Fast RF feedback may be desirable
– especially for TLEP where frev is lower,
detuning may drive coupled bunch modes
• Beamloading: “second Robinson”
instability
– loss of longitudinal focusing due to large
detune angle under strong beamloading
– occurs at low RF voltage with high beam
current
– seen in LEP2 at injection energy
– cured by using fast RF feedback on a few RF
stations
– an issue if we don’t have top-up injection
Becomes unstable
when VG is in
antiphase with IB
Second
Robinson
1st Robinson
Tentative conclusions
• We cannot use ILC technology “off the shelf”
– power coupler limitations
– loss factors and HOM damping
• Backing off in frequency to 700 MHz seems preferable
–
–
–
–
ongoing R&D at BNL, CERN, ESS for 704 MHz cavities and components
fundamental power couplers look feasible at > 200 kW CW
compatible with HOM damping scheme for eRHIC
high-power klystrons available
• Cryogenic power will probably fit into the envelope of the existing
LHC cryoplants (for LEP3)
• Open questions
– power coupler design
– HOM damping (especially for TLEP)
– low level RF & feedback requirements
An RF system for a circular Higgs factory such as LEP3 or TLEP is not without its
challenges but appears to be very feasible, especially as there are strong
synergies with other ongoing development projects.
Thank you for your attention!
• SPS 800 MHz TWC prototype feedback board
G. Hagmann BE-RF-FB
designer
Carnot ~150 @ 2K
Eff. ~ 30% of Carnot
Total wall-plug power for LHC
cryogenics = 40 MW